AREMA: Loading Behind Retaining Wall Supporting Tracks. 2

[CWEngineer]

I am in the process of designing a retaining wall, where a Railroad Track might be added behind it and I wanted to determine the kind of loads I need to add behind the wall. I obtained the following statement from "Manual for Railway Engineering, Volume 2, Structures, AREMA, Not Current Version": 2.2.3 Design Loads, c. Live Load. (2) The axle loads on structures may be assumed as uniformly distributed longitudinally over a length of 3 feet, plus the depth of ballast under the tie, plus twice the effective depth of a slab, limited, however, by the axle spacing.

Would it be possible to check if this is still applicable in the current code? Would providing a 3 feet "high" uniformly distributed infinite load be adequate?

Thanks

 

[civilperson]

Use 67 kips/axle for standard load axle and 79 kips/axle for heavy loading.(per Union Pacific) Railcar has four axles.

 

[minorchord2000]

I designed shoring for railroad tracks recently. I downloaded a free manual on shoring design from Union Pacific. Try them as a source.

 

[DWHA]

I have done some work with temporary soil retention systems near railroads. The railroad are very picky. The soil retention system I designed HAD to be designed for the Cooper E80 load using a strip loading. I initially tried to submit using a surcharge load slightly greater than what the cooper E80 came out to, but the railroad would not accept because they used the used the strip loading equation and got a larger force on the wall. I argued my case saying that the load that I was designing for was conservative. They said that I had to do it their way to get it approved. I don't think that they will allow the 3' surcharge.

I know that I used my Das book for the Strip Loading Eq.

 

[jorton]

I've done some shoring design for railroads as well. Norfolk Southern provides a table that gives the lateral loads at depth for various setbacks based on the Boussinesq Equation. It also allows you to use a simplified that is much easier to apply than the Boussinesq pressure loading. It is titled "Lateral Pressures from Coopers E-80 Train Loads", and it can be found at the link below. You may want to check the railroad for which you are designing to see if they have applicable design guides.

http://www.nscorp.com/nscportal/nscorp/Customers/Publications

 

[VoyageofDiscovery]

Great link

VOD

 

[CWEngineer]

Do you guys know how far the railroad tracks need to be from a retaining wall so that you can nelgect the loading from the railroad track on a retaining wall?

THANKS

 

[DWHA]

This may help.

 

[PEinc]

I would say that once the track is far enough away from the wall that the railroad influence line (or theoretical embankment line) does not hit the wall or sheeting (and extends below subgrade), then you can ignore the surcharge.

 

[CWEngineer]

Just want to confirm the following:

Is the theorethical embankment line,the 2H:1V line shown in the sketch.

If I start my embankment 15'-6" from the center line of the closest track and draw my 2H:1V embankment Sloping down and if this line is below the wall or sheething then I can ignore the surcharge.

THANKS

 

[PEinc]

I would say yes. In fact, if your excavation is above the 2:1 line, you do not need sheeting. Therefore, there should not be any RR surcharge either (even though Boussinesq will give you one). However, if you are above this line and you still want to build some type of wall, there might be other surcharge pressures you need to apply -such as for other vehicles (cars, trucks) or materials stored alongside the tracks, behind the wall.

 

[PEinc]

PS, make sure you check for a similar sketch for the particular railroad you are dealing with, or any other railroad(s) that may share the same tracks. Sometimes, freight trains from one rail company use the tracks of another rail company. You may need to use the more critical conditions. Also, some railroads require you to design for Cooper E80 while others require E80 plus 50%.

 

[CWEngineer]

Thanks, I am dealing with BNSF so this Figure is applicable. Currently, the theoretical embankment line falls below my retaining walls, so I can ignore the surcharge from the railroad track.

I had one more question, say my retaining wall would have fallen within the embankment line (2H:1V), is there a standard depth that if the wall is below that depth, the surcharge can also be neglected?

THANKS

 

[PEinc]

Not in my recent experience. In passed years, there were walls I designed which were above a 45 degree line coming down from the end of the rail ties and walls where the ties were beyond the active failure plane. For these walls, I have had various railroads accept no application of a rail surcharge load. Those days seem to be gone.

 

[JStructsteel]

From AREMA, section 8-5.3.1b, surcharge is as quote- "With increased depth, the width for distribution can be increased on slopes of 1 horizontal to 2 vertical, with surcharge loads from the adjacent tracks not being permitted to overlap"

To me its 2:1 from the bottom of the tie.
What do you guys think?

 

[PEinc]

The particular railroad will usually tell you what surcharge loading they will insist on (despite what AREMA may say). AREMA will probably be considered as the minimum required surcharge load.